Soil Carbon Flux And Storage Were Measured Across A Chronosequence Of Secondary Forests Dominated By Betula Platyphylla In Xiaoxing'an Mountain, China

Soil respiration (SR) and belowground carbon storage are the two important roles in both local and national carbon budgets. The spatial and temporal changes in soil surface CO2 flux, the major CO2 source to the atmosphere from terrestrial ecosystems, directly influence the local and regional carbon budgets. Soil organic carbon, is the largest carbon storage pool of forest ecosystems in high latitude regions, playing a key important on component of ecosystem carbon budgets. Soil surface carbon flux and storage were measured at three secondary Betula platyphylla forests at different succession stages (20a,36a,82a) at the Xiaoxing'an Mountain, Northeastern China, which of great significance in understanding the effects of stand ages on forest source/sink, regional forest carbon budget and forest carbon management. In this study, we used infrared gas exchange analyzer (Li-Cor 6400) to measure soil respiration and related factors. Soil profile at different depth was used to estimate the content of soil organic carbon and carbon storage. Our results were as follows:In this study, we conducted soil flux measurement during the growing season (days 132-295) in 2008, and found that the soil respiration increased with stand ages. The mean soil respiration were 3.26μmol·m-2·s-1,3.78μmol·m-2·s-1 and 4.26μmol·m-2·s-1 in the three Betula platyphylla forests:20a,36a and 82a, respectively. The Q10 values of SR derived from soil temperature dependence function were 3.19,2.86 and 2.51 for the three Betula platyphylla forests:20a,36a and 82a, respectively. Soil temperature at 5 cm significantly (P<0.001) influenced the soil respiration. It was found that the soil respiration increases exponentially with soil temperature. In addition to soil temperature, the content of soil organic carbon and root biomass significantly (P<0.05) influenced the soil respiration. There was a positive significant (P<0.001) relationship between soil respiration and soil organic carbon (SOC) at a depth of 0-10 cm, and SOC concentration at 0-10 cm horizon explained 87% of variations in soil respiration. Rates of SR were linearly related to root biomass across the three Betula platyphylla forests at different succession stages, with fine roots (<1 mm) contributing proportionally more to total soil respiration.The contents of soil organic carbon (at the depth of 0-50 cm) varied 10.2～84.5 g-kg-1, 29.3～75.9g·kg-1 and 36.4～130.7 g·kg-1 in the three Betula platyphylla forests:20a,36a and 82a, respectively. And the soil carbon density varied 14.7 kg·m-2,18.1 kg·m-2 and 18.7 kg-m 2 in the three Betula platyphylla forests:20a,36a and 82a, respectively. Our results also showed that the contents of soil organic carbon and soil carbon density decreased with the increased of soil depth; the contents of soil organic carbon and soil carbon density increased with stand ages.